This invention relates to surgical staples formed from an extruded "polymeric wire." . The term "wire," as used in describing this invention, includes both polymeric and metallic monofilaments. It has been found that wire (or monofilament fiber) extruded from polymer that is normally rigid at in vivo conditions can be used to form a surgical staple. The formation of a staple using the polymeric wire is accomplished using standard methods employed in the manufacture of metallic staples used in the surgical staple industry. Normally rigid polymers, when oriented by extrusion into polymeric wire according to this invention, have enhanced ductility in flexure. The terms "ductile" and "ductility" as used in describing this invention denote the property of permanent deformability, or plasticity, which may result from processes such as crazing or yielding. Specifically, ductile polymeric wires, when bent, will retain a large portion of the bend angle permanently (note that it is not required that the polymeric wires of this invention be ductile in tension along the fiber axis, only in bending or flexure) and the application of work is required to unbend the bent wire. This property can be used to form surgical staples simply by bending the polymeric wire as is done for metallic staples. This type of staple has great advantages over the types of staples in use today.
The current commercially available plastic staples are two-piece, injection molded devices. These staples are relatively large due to the need for the incorporation of an interlocking mechanism for joining the two staple pieces. The staples of the present invention have no requirement for an interlocking mechanism because the final form of the staple is accomplished simply by bending the polymeric wire, exactly as is done for metallic wires. The polymeric wire, not being as stiff as metal, requires a somewhat larger diameter to provide adequate holding power, but the final size is much more acceptable to the surgeon than the currently available plastic surgical staples.
The polymeric wire also has advantages over metallic wire. Metallic staples are known to be highly radiopaque, causing difficulties in reading X-ray images (both conventional and CT (Computed Tomography) scanning images) as well as MRI (Magnetic Resonance Imaging) images due to what is known as the "starburst effect," a result of the high contrast of the metal to the tissue. These small areas of high contrast can cause difficulties in interpreting these images for subtle diagnostic purposes. Most polymers are known to be much more radio-transparent than metals. The reduced contrast between polymeric staples and tissue using these radio-imaging techniques eliminates the starburst effect. An additional advantage of polymeric staples over metal is that the polymeric staples can be formed from bioabsorbable polymers; thus, eliminating the risk of long term foreign body reactions of the tissue or staple migration that may be encountered with metal staples.
The patent and medical literature dealing with metallic staples and their uses in surgery is quite extensive. A review of surgical procedures involving internal staples and stapling devices can be found in "Stapling in Surgery", F. M. Steichen and M. M. Ravitch, Year Book Medical Publishers, Inc., Chicago, 1984, which is incorporated herein by reference. Because of the obvious differences between metallic and polymeric staples, a detailed review of metallic staples is not necessary to illustrate the uniqueness of the present invention.
With regard to polymeric staples, a number of patents and journal articles have appeared which describe the advantages of polymeric materials for staple applications. The majority of these publications describe a preference for absorbable polymers. The following U.S. patents are background to the present invention described in this application: U.S. Pat. Nos. 4,994,073, 4,976,909, 4,889,119, 4,844,854, 4,839,130, 4,805,617, 4,744,365, 4,741,337, 4,719,917, 4,671,280, 4,646,741, 4,612,923, 4,610,250, 4,602,634, 4,589,416, 4,573,469, 4,532,926, 4,523,591, 4,513,746, 4,428,376, 4,402,445, 4,317,451, 4,272,002, 4,060,089, 4,006,747. All of these patents are incorporated herein by reference.
Almost all of the above patents describe various polymeric materials for use in two-part, molded (not extruded) snap-together staples of various designs. These staples are not made from extruded, oriented polymeric wire and are not bent to form the final, implanted, staple shape. Two patents, U.S. Pat. No. 4,976,909 and U.S. Pat. No. 4,671,280, describe a two-piece staple where one of the components is formed from an extruded, "oriented crystalline polymeric material". The final, implanted, staple form is achieved by mating the extruded portion with a molded portion, not by bending the oriented component. Two of the above cited patents, U.S. Pat. No. 4,428,376 and U.S. Pat. No. 4,317,451, describe one-piece staples made of absorbable or non-absorbable polymers. These patents describe a mechanical looking-hinge mechanism to hold the staple legs in their final configuration. Application of the devices described in these patents to tissue is accomplished by bending at the hinge point until the locking mechanism engages. The devices described are not formed from extruded polymeric wire and are not formed or applied by bending an extruded polymeric wire. Another patent, U.S. Pat. No. 4,994,075, describes a one-piece molded device that uses two barbed prongs to hold the tissue. This device is not formed from extruded polymeric wire and it is not formed or applied to tissue by bending.
The disclosure in the patent application, U.S. Ser. No. 07/548,802 filed on Jul. 6, 1990, now U.S. Pat. No. 5,080,665 by P. K. Jarrett, D. J. Casey and S. L. Peake, entitled "Deformable, Absorbable Surgical Device" and assigned to American Cyanamid Co., Stamford, Conn. 06904-0060 is incorporated herein by reference. This patent application describes, e.g., in claims 1 and 10, a clip or staple manufactured from a copolymer or blend.